1. Field of the Invention
This invention relates generally to computer memory devices and relates more particularly to efficient defect management in a magneto-optical data storage system.
2. Description of the Background Art
Reliable storage and retrieval of digital information is a significant concern for designers and users of computer systems. High capacity random access storage systems are often based on magnetic disk technology. Magneto-optical data storage systems offer many advantages over conventional magnetic data storage systems, but also have some unusual problems.
The recording materials used in magneto-optical data storage systems are chemically unstable and thus have different defect characteristics than recording materials used in magnetic data storage systems. Defects in magneto-optical recording materials are nominally circular and may grow in size by a factor of two over the life of the magneto-optical data storage system. Such defects therefore may damage or destroy more recording surface area long after manufacture. These unique complexities present additional problems in magneto-optical defect management. Hardware and software previously developed for magnetic data storage systems is generally incapable of managing defects with the unique characteristics (number, size, and growth) of magneto-optical recording materials. Efficient defect management in a magneto-optical data storage system therefore requires an improved apparatus and method.
In accordance with the present invention, an apparatus and method are disclosed for efficient defect management in a magneto-optical data storage system. In one embodiment of the present invention, a host computer sends a command via SCSI interface to write data and the data storage method sequence begins. The interface responsively writes the logical address and contents of each data sector to be stored into a memory. A microprocessor then scans the memory to determine if all data sectors have been processed. If not, the microprocessor chooses an intended physical address at which storage of each data sector is to begin. A search engine next scans a zone table and returns the physical address of a serviceable data wedge to the microprocessor. The contents of the zone table are initially determined at the time of magneto-optical data storage system manufacture, so that all defective data wedges may be identified and subsequently skipped to thereby eliminate read-after-write data verification delays.
Next, a read/write controller orders a servo controller to move the read/write head to the beginning of the serviceable data wedge. If a split (border between two data sectors) exists in the data wedge, the read/write controller waits for the split to arrive, and then sets a write gate signal to enable writing. If the end of the data wedge is reached, then the read/write controller disables the write gate signal and commands the servo controller to move to the next data wedge. If the end of a data sector is reached, then the read/write controller disables the write gate signal and the microprocessor updates the zone table. The method steps for reading data are analogous to the foregoing method steps for writing data.
The invention stores a map of the present and predicted defective physical addresses of a recording disk, and skips defective data wedges to more completely utilize the non-defective recording surface area available on a given track. The invention also stores groups of physical addresses that share defects. Storage of defect groups decreases the number of entries in the map of defective physical addresses and increases the effective defect management capacity of existing hardware and software. Therefore, the present invention more efficiently manages defects in a magneto-optical data storage system.